1. Technical Field
This invention is directed toward a new camera design. More specifically, this invention is directed toward a new omni-directional camera design that provides an improved viewpoint for video capture of meetings compared to prior camera designs.
2. Background Art
Video conferencing systems have had limited commercial success. This is due to many factors. In particular, there are numerous technical deficiencies in the video conferencing systems to date. Poor camera viewpoints and insufficient image resolution make it difficult for meeting participants to see the person speaking. This is compounded by inaccurate speaker detection (especially for systems with pan-tilt-zoom cameras) that causes the camera not to be directed at the person speaking. Additionally, poor video compression techniques often result in poor video image quality and a “choppy” image display.
Three common methods exist to capture video data: pan/tilt/zoom (PTZ) cameras, mirror-based omni-directional cameras, and camera arrays. While PTZ cameras are currently the most popular choice, they have two major limitations. First, they can only capture a limited field of view. If they zoom in too closely, the context of the meeting room is lost; if they zoom out too far, people's expressions become invisible. Second, because the controlling motor takes time to move the camera, the camera's response to the meeting (e.g., switching between speakers) is slow. In fact, PTZ cameras cannot move too much or too fast, otherwise people watching the meeting can be quite distracted by the noise and motion of the camera as it adjusts its viewpoint.
Given these drawbacks and recent technological advances in mirror/prism-based omni-directional vision sensors, researchers have started to rethink the way video is captured and analyzed. For example, BeHere™ Corporation provides 360° Internet video technology in entertainment, news and sports webcasts. With its interface, remote users can control personalized 360° camera angles independent of other viewers to gain a “be here” experience. While this approach overcomes the two difficulties of limited field of view and slow camera response faced by the PTZ cameras, these types of devices tend to be too expensive to build given today's technology and market demand. In addition, these mirror prism-based omni-directional cameras suffer from low resolution (even with 1 MP sensors) and defocusing problems, which result in inferior video quality.
In another approach, multiple inexpensive cameras or video sensors are assembled to form an omni-directional camera array. For example, one known system employs four National Television System Committee (NTSC) cameras to construct a panoramic view of a meeting room. However, there are disadvantages with this design. First, NTSC cameras provide a relatively low quality video signal. In addition, the four cameras require four video capture boards to digitize the signal before it can be analyzed, transmitted or recorded. The requirement for four video capturing boards increases the cost and complexity of such a system, and makes it more difficult to manufacture and maintain. Another issue with these types of cameras is that they tend to be larger and when placed in the middle of a conference table they can be obtrusive and block the meeting participants views of each other due to their larger size.
Other camera systems have employed mirrors to achieve 360 degree coverage of a meeting room by creating camera arrays wherein the cameras are disposed in a back-to-back circular fashion directed at a number of mirrors which results in a common virtual center of projection. That is, the effective distance D between the centers of projections of all of the cameras in the array, is zero. The distance D can be modified by varying the angle at which a given mirror is positioned relative a given camera. The center of projection of a camera is defined as point of which one can rotate the camera around and only get a rotational transformation, and no translational transformation. For camera systems employing mirrors, the virtual center of projection corresponds to where the center of projection of the camera would have to be if there was no mirror to capture the same portion of the surrounding scene. When the virtual center of projection for all cameras in the array is common, there is no parallax error, no matter how far or how close the surrounding objects to be captured are from the camera. The goal for these camera arrays employing mirrors is to provide a seamless panorama. In this type of camera array, images must be stitched together to create a panoramic view of the area photographed. Having no parallax error allows the images to be readily stitched with no ghosting or other errors. When the common virtual center of projection is zero, however, these camera systems are usually quite large, because in order to obtain the aforementioned common center of projection it is typically necessary to employ very large mirrors. This makes this type of camera undesirable for video conferencing applications because when placing it in the center of a conference room table it is obtrusive and annoying to meeting participants. An example of such a camera system employing mirrors with a common virtual center of projection was Circarama™, a special presentation system that was used at Disneyland®. The spectators stood in the middle of a circle viewing a 360-degree panorama on a surround screen 8 feet high and 40 feet in diameter made up of eleven panels. The original negatives were made on eleven 16 mm cameras arranged in a concentric circle. The prints were projected by a ring of interlocked 16 mm projectors. In that camera, the mirrors are used to create a virtual center of projection for each camera, which is identical for each camera.